1. Field
Aspects of the present invention generally relate to an image processing apparatus, an image processing method, a recording apparatus, and a non-transitory computer-readable storage medium storing a program, which are provided for recording an image on a recording medium.
2. Description of the Related Art
There is an inkjet recording apparatus including a nozzle array in which a plurality of ejection openings (nozzles) capable of ejecting ink are arranged. One of factors of not being able to obtain a high-quality image in such an inkjet recording apparatus may be density unevenness of an image resulting from variations in ejection characteristics of a recording head. In an inkjet recording apparatus including a plurality of recording elements (nozzles), the ejection characteristics of the individual recording elements vary, and thereby density unevenness may occur in a recorded image. The variations in ejection characteristics of the recording elements are classified into variations in a landing position of ink and variations in an ejection volume, which may result from variations in a heating value of a heater that heats ink, variations in a nozzle aperture, and so forth. Also, the amounts of ink ejected from the individual recording elements may vary due to variations in a heating value of a heater caused by change over time or variations in viscosity of ink caused by a difference in an environment where the apparatus is used. Such density unevenness becomes significant in accordance with an increase in the size of the recording head, and use of a multihead.
To address such variations in ejection characteristics of a recording head, a multipass recording method is available. In the multipass recording method, an image is recorded through a plurality of scanning operations by using more nozzles, and thus influences of individual nozzles on a recording medium are reduced, and thereby density unevenness is reduced.
As another method for reducing density unevenness, head shading correction is available. In head shading correction, a test pattern recorded by using a recording head and having an even density is read, and a correction table is created for correcting the density values of pieces of image data corresponding to individual nozzles so that density unevenness is reduced. As a result of correcting the pieces of image data corresponding to the individual nozzles by using the correction table, an image without density unevenness is stably output.
U.S. Pat. No. 6,874,864 discloses, in addition to the multipass recording method, a method for making it difficult to visually recognize a boundary streak by setting a recording ratio of a nozzle positioned at an end portion of a nozzle array to be lower than a recording ratio of nozzle positioned at a portion other than the end portion.
Also, a calibration technique is available as a technique of reducing color unevenness resulting from variations in ejection characteristics of individual nozzle arrays or recording heads. Japanese Patent Laid-Open No. 2004-167947 describes a method for measuring the density of a patch by using a scanner that is provided on a carriage to read the patch, and automatically performing color unevenness correction (calibration) on the basis of the measurement result. In this method, calibration is performed for individual recording heads corresponding to individual ink colors, and density correction values of individual gradation levels of individual ink colors are obtained.
In the case of performing multipass recording of two passes or more by using a head shading correction method according to the related art, if the usage ratio of each nozzle varies in individual rasters when one raster is recorded by using a plurality of nozzles, the processing load for performing appropriate correction is high. It is necessary to generate a correction table by recording and measuring a test pattern of even density for each number of passes and each type of mask pattern, and thus a large amount of data processing and a large capacity memory are necessary.
In the method disclosed in U.S. Pat. No. 6,874,864, the usage ratios of a plurality of nozzles used for recording vary among individual rasters, and thus more significant density unevenness occurs. In the method disclosed in Japanese Patent Laid-Open No. 2004-167947, it is impossible to reduce color differences resulting from variations in ejection characteristics of individual nozzles.